Twin Towers Memorial Suggestion
Fred Bernstein of New York City has put an excellent idea for a Twin Towers memorial on his website. I suggest checking out his web site to see his visuals and full description.
But the quick of it is to build two docks out over the water that each are the exact size (width and length, not depth) of the fallen tower they respectively represent. Visitors would walk down the length of the dock as if they were a pier on a beach, and as they passed each "floor" of the building, they would be able to hear and read descriptions of that businesses and individuals worked on that floor.